RNA interference (RNAi) is a mechanism capable of inhibiting the expression of a gene in a highly specific and efficient manner, in which degradation of the mRNA of a target gene is induced by introducing a double-stranded RNA, which comprises a sense strand having a sequence homologous to the mRNA of the target gene and an antisense strand having a sequence complementary to the mRNA of the target gene, into cells or the like, thereby inhibiting the expression of the target gene.
An siRNA that induces this RNA interference is a short (19-21 bp) double-stranded RNA capable of inhibiting the expression of a target gene in a sequence-specific manner, and is currently receiving attention as a therapeutic agent against various diseases, including cancer difficult to treat, viral infections, and hereditary diseases, thanks to its high efficiency and target specificity. For the development of effective therapeutic agents based on an siRNA, various problems associated with stability, silencing efficiency, immune responses, off-target effects and the like, are required to be solved, and among them, effective in vivo delivery is considered most difficult to achieve. An siRNA cannot pass through the cell membrane, because it is highly negatively charged due to its phosphate backbone structure. In addition, because of its small size, the siRNA is quickly removed from blood, and thus it is difficult to deliver the siRNA in an amount sufficient for inducing RNAi to a target area.
In the case of in vitro delivery, many high-efficiency delivery methods that use cationic lipids and cationic polymers have been developed (Sioud M, Sorensen D R Cationic liposome-mediated delivery of siRNAs in adult mice. Biochem Biophys Res Commun 2003; 312: 1220-1225). However, in most cases, in vivo delivery of siRNAs is difficult to achieve with high efficiency, unlike in vitro delivery, and the efficiency of delivery of siRNAs decreases due to their interactions with various proteins in vivo (Bolcato-Bellemin A L, Bonnet M E, Creusat G, et al. Sticky overhangs enhance siRNA-mediated gene silencing. Proceedings of the National Academy of Sciences of the United States of America 2007; 104: 16050-16055). In addition, siRNAs are highly accumulated in a specific organ such as liver or lung, which is not a diseased area, depending on the composition of delivery vehicles, thus inducing toxicity.
Meanwhile, connective tissue growth factor (CTGF/CCN2) is known as a matricellular protein that plays an important role in the differentiation, growth, migration, ECM production, adhesion and the like of cells. In the case of chronic fibrotic disorders that induce fibrosis in various organs to cause damage to the organs, it was found that CTGF is overexpressed in tissues in which fibrotic disorders occur. Also, the relationship between CTGF and fibrosis in the skin has been relatively well studied. In addition, it was observed that the expression of CTGF in a normal skin was inhibited to the basal level, but temporarily increased when the skin was wounded. On the contrary, in the case of keloid or localized sclerosis, it was observed that the overexpression of CTFG was maintained even after wound healing, and when the expression of CTGF was inhibited using an antisense strand or the like, fibrosis and keloid production were inhibited, suggesting that CTGF plays an important role in fibrosis and keloid production (Sisco M, Kryger Z B, O'Shaughnessy K D, et al. Antisense inhibition of connective tissue growth factor (CTGF/CCN2) mRNA limits hypertrophic scarring without affecting wound healing in vivo. Wound Repair Regen 2008; 16: 661-673. DOI: WRR416 [pii]). Pathologically, it is known that a full-length CTGF molecule is involved in a condition in which the hyperproliferation of connective tissue cells and the excessive deposition of extracellular matrix are present. In addition, it is known that CTGF is also involved in conditions associated with the migration and proliferation of endothelial cells and angiogenesis. Examples of diseases and disorders associated with such conditions include the fibrosis, cancer and related diseases and disorders of the skin and major organs, for example, systemic sclerosis, angiogenesis, atherosclerosis, diabetic nephropathy, and renal hypertension. Also, CTGF is known to be useful for wound healing, connective tissue repair, and bone and cartilage repair. In such terms, CTGF was disclosed as an inducer of bone, tissue or cartilage formation disorders such as osteoporosis, osteoarthritis or osteochondritis, arthritis, skeletal disorder, hypertrophic scar, a burn, hemagiectatic hypertrophy, or sound healing (see, for example, U.S. Pat. No. 5,837,258).
Accordingly, the present inventors have made extensive efforts to provide a novel, RNAi-inducing nucleic acid molecule that can be effectively delivered in vitro and in vivo and has cell-penetrating ability, and as a result, have found that, when the phosphate backbone of at least one nucleotide in an RNAi-inducing double-stranded nucleic acid molecule is substituted with phosphorothioate and a lipophilic compound is conjugated to the nucleic acid molecule, the nucleic acid molecule exhibits high target gene silencing efficiency even in vivo without needing a separate intracellular delivery vehicle and, at the same time, has high cell-penetrating ability, thereby completing the present invention.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present invention, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.